The harmonic balancer is held on by the big bolt in the crankshaft (27mm). Mine has 2 round keys that keep it from rotating relative to the crankshaft. The allen screws hold the pulley onto the balancer. Sounds like your pulley sheared off the bolts and is no longer attached. The balancer to the crank fit is tight, but it will come off with a puller. I used a harmonic balancer puller that I bought at Advance Auto ($14). However, using a tool like this requires that the pulley screw holes to be available (which yours aren't). So....if you can't get at least 3 of them out, you'll have use a pulley puller or large gear puller. Like someone cautioned above: Make sure you have marked the balancer relation to the crankshaft; it is balanced and marked; it has go on like you remove it. There are some other threads on reinstallation - search and read them - you don't want to mess up your crankshaft.

Good luck!

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold